The AdS/CFT correspondence gives a simple way to study strongly correlated systems [1]}, [2]}, [3]}. In the framework of AdS/CFT, one can relates the weakly coupled classical gravity theories to the strongly coupled quantum many-body systems. So it provides a new approach to calculating observables in these strongly coupled many-body system. In particular, one can perturb the electric field and thermal gradients around black hole background to calculate the transport coefficients such as conductivities in the strongly correlated systems on the boundary.
